H. Polysperma a noxious weed? Yeah, I would think so.
My 75 gallon tank has been up now for maybe 3 weeks. Most of the plants are just getting established. The algae is having no problem getting established, but that is another story. When I went over to the tank today to cycle it and see what needed to be pruned, the sunset hygro had DOUBLED in volume, overshadowing all the plants around it and sending out tons of horizontal runners. In about three weeks of time, I had to trim off a TON of that stuff. I can see why you wouldn't want that crap in your local waterways, hehheh.
Two 1 GA desktops, a 5 gallon, a 2.5 gallon, a 10 gallon, a 20 gallon, a 25 gallon, and two 75 gallon tanks, all planted.
I am an expert on algae, so ask me if you have questions. I know how to grow it, just not how to get rid of it.